The present invention relates to an optical lens used for white light in a camera, a projector, a lighting device, and the like, and an optical device using the optical lens.
JP-A-2001-249271 is a related art in the field of the present invention. JP-A-2001-249271 discloses that “An objective lens 10 is a single lens formed of resin and both surfaces of which are aspheric, and a diffractive lens structure is formed on one lens surface 11 as an annulus-like pattern around an optical axis. At least one of the lens surfaces 11 and 12 is aspheric, and the objective lens 10, in serving as a refractive lens, excessively corrects spherical aberration. The diffractive lens structure is designed to have a predetermined spherical aberration based on steps formed at boundaries between annuli in the direction of an optical axis as in a Fresnel lens an that, for the lens as a whole, the spherical aberration does not change even when the refractive index changes.” (see Abstract).
Furthermore, JP-A-2013-182264 is another related art in the field of the present invention. JP-A-2013-182264 discloses “A method for manufacturing a transmissive screen, including a step of preparing a first masking sheet 30 stuck to a surface of a Fresnel lens sheet 20 opposite to a surface of the Fresnel lens sheet 20 on which a Fresnel lens portion 22 is formed, a step of heating and softening a Fresnel lens sheet 10 with a masking sheet, and a step of placing the Fresnel lens sheet 10 with the masking sheet on a first mold 40 with a first mold surface 41 that is at least partly curved so that the first masking sheet 30 corresponds to the first mold surface 41 side and sucking air through a first suction hole 42 present in the first mold surface 41 to mold the Fresnel lens sheet 20 with the masking sheet such that the Fresnel lens sheet 20 has a curved surface.”
Furthermore, JP-A-2013-200367 is another related art in the field of the present invention. JP-A-2013-200367 discloses that “In a Fresnel lens 1, a first surface 10 is a flat surface, and a second surface opposite to the first surface 10 has a plurality of (in an illustrated example, three) second lens surfaces 20. In the Fresnel lens 1, aspheric surfaces providing the respective lens surfaces 21 have different central axes CAO, CA1, and CA2, and the positions of foci F(FO), F(F1), and F(F2) of the lens surfaces 21 are misaligned with one another on one image surface I. An optical detector includes the Fresnel lens 1.”